As a high permittivity ceramic material for capacitors, there have been proposed various dielectric ceramic compositions mainly comprising barium titanate. For example, Japanese Pat. laid open No. 58-60671 discloses a dielectric ceramic composition of a ternary system, Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3. Such a dielectric ceramic composition makes it possible to produce ceramic capacitors with a small change rate of capacitance on temperature, which meets B characteristics established by Japanese Industrial Standard (JIS), but its dielectric constant is small at room temperature and of the order of about 2000, thus making it difficult to produce ceramic capacitors with a large capacitance-to-volume ratio.
On the other hand, there have been known complex perovskite lead compound dielectric ceramic compositions having a dielectric constant of not less than 10000 and a low sintering temperature of not more than 1050.degree. C. However, if such a composition is applied to monolithic ceramic capacitors, they have a large temperature change rate of capacitance ranging from -50% to +30% in the operating temperatures of -25.degree. C. to +85.degree. C.
Thus, there is an increasing demand of development of a dielectric ceramic composition with a small temperature change rate of capacitance and high dielectric constant.
The ceramic capacitors are generally produced by the steps of preparing ceramic green sheets, forming a metal paste layer for an internal electrode on one flat surface of each ceramic green sheet, stacking and pressing the green sheets to form a multilayer green ceramic body, and firing it to form a monolithic sintered ceramic body with internal electrodes. The dielectric ceramic composition containing lead compounds is generally fired in an oxidizing atmosphere as its insulating characteristics are lowered when fired in a reducing atmosphere. Since internal electrodes are fired together with the dielectric ceramic composition, a material for internal electrodes is required to have a high resistance to oxidation and high melting point, as well as not to react with the dielectric ceramic material during firing. To this end, noble metals such as platinum, or noble metal alloys such as silver-palladium alloys have been used as a material for internal electrodes.
However, the use of noble metals results in increase of production cost of the monolithic ceramic capacitors. If a silver-palladium alloy is used as a material for the internal electrodes, it causes migration of silver into the ceramic dielectric layers, resulting in lowering of the electrical characteristics of the produced capacitors. In addition, the silver-palladium alloy causes increase in equivalent series resistance of the capacitor because of its low conductivity.
To solve these problems, use of copper or copper alloys as a material for internal electrodes are considered as these materials are high in conductivity but low in price. However, the dielectric material is required to be fired in a reducing atmosphere at a low temperature as copper and its alloys have a low melting point and are easily oxidized in the oxidizing atmosphere. For these reasons, it is required to develop a dielectric ceramic composition which possesses high dielectric constant and a high specific resistance even if fired in a reducing atmosphere.